Aircraft undercarriage, or landing gear, are wheels on which aircraft move when on the ground.
In modern aircraft, undercarriage wheels are usually arranged in a tricycle formation, having a wheel or group of wheels under each wing, and a wheel or group of wheels under the nose of the aircraft. The wheels generally retract into a bay inside the fuselage during flight. This is necessary to eliminate the drag which they would otherwise cause. Doors are sometimes attached to the bay. These doors open to let the undercarriage wheels out, and close to protect the wheels and reduce drag during flight. The undercarriage wheels are generally attached to the fuselage via retractable support struts, such as telescopic, liquid filled struts. Shock absorbing mechanisms are usually built into the struts. Undercarriage wheel tires are generally high profile pneumatic tires. Fan blades, air scoops or small motors are known in the art for causing the wheel to turn at the speed of travel, prior to landing, to reduce wear in the tires caused upon landing.
The use of separate motors to move aircraft on the ground is helpful since it avoids using the aircraft turbines or a separate tug to move the aircraft.
U.S. Pat. No. 3,711,043 to Cameron-Johnson discloses an aircraft drive wheel having a fluid-pressure-operated motor housed within the wheel and two planetary gear stages housed in a gear box outboard of the motor, the final drive being transmitted from a ring gear of the second gear stage, which is inboard of the first stage, to the wheel through an output drive quill coupled, through a disc-type clutch if desired, to a flanged final drive member surrounding the inner end of the gear box and bolted to the wheel.
U.S. Pat. No. 3,977,631 to Jenny discloses a wheel drive motor selectively coupled to an aircraft wheel through a rotatably mounted aircraft brake assembly in order to drive the wheels of an aircraft. The normally non-rotating stator portion of a conventional aircraft brake assembly is rotatably mounted about the wheel axle and is rotatably driven through a planetary gear system by the wheel drive motor.
A solution disclosed in PCT application WO2005/035358 discloses a mesh connected high phase order induction motor, situated in close proximity to, and preferably within, the nosegear. The mesh connection enables variable inductance so that the machine has a range of speed/torque profiles available.
European Patent No. 0 756 556 B1 to Giovanardi and Centofante discloses an aircraft having wheel driving means associated with at least one of the wheels of the landing gear. A motor powered by the auxiliary power unit of the aircraft is used to drive the wheels of the landing gear. The assembly comprises an electric or hydraulic motor in operative connection with a differential gear assembly, each wheel being mounted on an axle in forward operative connection with a respective half-shaft of the differential gear through a free wheel mechanism.
All of the solutions mentioned above require extra space to be occupied close to the undercarriage wheel, requiring extra space in the bay into which the undercarriage retracts. Space in this area is severely restricted. The shape and volume of the bay into which the undercarriage wheel retracts is of fixed size and cannot easily be altered. Further, using a bigger wheel and a bigger tire, in order to house a motor powerful enough to move the plane unassisted, will increase the mass of that part of the undercarriage, which may have deleterious effects on the balance and handling of the aircraft.
U.S. Pat. No. 4,267,992 to Harper discloses a tire and wheel assembly in which a low profile pneumatic tire having sidewalls which deflect inwardly under load and a wheel having a rim featuring a narrow central channel and extended rim flanges form the combination. This reduces the total assembly diameter required for a given unit load thereby reducing or eliminating wing surface bulges for vertically stowed wheels as well as reducing the drag profile of the wheel well area.